Report error location in tree

[blaggacao]

https://github.com/ekala-project/modules/blob/master/src%2Fdefault.nix#L55

We should find a way, potentially through an upstream patch, to show the error location (unsafely) within the current working tree, rather than (or: in addition to) within the nix store.

[nrdxp]

I have the beginnings a an error origin parser that actually shows you the location in the toml file, with line numbers. It's actually quite nice, but it'll have to be abstracted to be more generally useful:

atom/src/atom/errors.nix

Line 26 in 9f84d5b

missingName =

[nrdxp]

So now that eka is further along, I realize we want to avoid doing any sort of complex parsing in Nix code directly. Rust has excellent toml parsing and error reporting already, so for errors directly in the manifest, it'd be much better to report them as early as possible, before even entering a Nix evaluation context.

As for knowing our current location within the module system for debugging purposes, #36 is an excellent start. We really just need to ensure some consistency with eka's verbosity flag, so we might want to add a few different levels, like: info, debug, trace at a minimum?

In any case, all that's left to do there is clean up the implementation, it already reports location information quite nicely.